This invention relates to a flow guide for ship propellers in which the propeller shafts are rotatably supported adjacent the propellers by propeller brackets. The flow guide has a sectioned and arcuate configuration and is arranged transversely to the direction of flow upstream of the propeller. The arcuate guide extends at least between a pair of arms of the propeller bracket which arms project radially from the propeller bracket nut, in which the shaft is rotatably mounted, to the ship's hull.
In the case of ships with twin propellers, the propeller shafts usually project rearwardly a substantial distance from the hull, and consequently it is necessary to support the propeller shafts adjacent their ends. This is usually effected by propeller brackets having at least two arms which extend between the propeller bracket nut, adjacent the propeller, and the ship's hull. The propeller shafts are guided inclinedly relative to the flow direction by the propeller brackets which brake the flow velocity and increase thereby the wake which is produced by the marginal layer of the ship's hull and the separation of the flow. The irregularity of the flow to the propeller results in a reduction in its efficiency. The region of such low flow velocity is at the same time a region of high local propeller stress. Consequently, stronger pressure pulses are exerted on the adjacent areas of the ship's hull surface. Due to the high tangential stress and the relatively small water column above this area, this region is particularly endangered by cavitations.
Various constructive measures have been attempted in the prior art for the purpose of making the flow velocity to the propeller more uniform. Propeller brackets have been utilized which have a single arm extending between the propeller bracket nut and the ship's hull. The disadvantage of this construction is that a single arm necessarily has a large cross-sectional area.
Shafts of the Grim type, in which the propeller shaft is guided in a resilient pipe at the end of which, facing the propeller, a supporting bearing is located, have been used.
The arms of the propeller brackets have been shaped as guide surfaces to form a nozzle arrangement. In some instances the arms of the propeller brackets have been formed to provide a counter twist to the flow.
Attempts have been made to shield the ship's hull against the propeller affect by means of a metal sheet arranged in the direction of flow between the propeller and the skin of the ship. This arrangement does not eliminate irregularity in the flow, though the pressure pulses are intercepted.
Attempts have been made to utilize a horizontal guide surface arranged between the propeller bracket nuts or at the height of the upper blades of the propeller. This guide surface uses, to the extent it is arranged in the flow to the propeller, the initial twist for propulsion purposes so that substantial power savings can be effected. This guide surface does, however, not accelerate the flow to the upper propeller blades. Rather a delay affect will occur which results in the upper propeller blades being stressed more heavily and in the emission of stronger pressure pulses so that stronger vibrations are created. The German periodical "Hansa", 1970, No. 18, pages 1519-1524, describes such a horizontal guide surface for twin propeller arrangements.